Au Pd Research Articles

Gold–Telluride–Palladium Mineralization, a New Type of Mineralization in Gabbro-Dolerites of the Pai-Khoi Ridge (Yugor Peninsula, Russia)

Abstract —Data on gabbro-dolerite pyrite–chalcopyrite–pyrrhotite, quartz vein sphalerite–chalcopyrite, and associated early and late gold–telluride–palladium mineralization of the Krutoi ore occurrence (Pai-Khoi Ridge, Yugor Peninsula) are presented. The early (magmatic) gold–telluride–palladium mineralization is represented by minerals of the ternary system Ag–Au–Cu, palladium antimonides and stibiotellurides, and platinum arsenides, and the late (hydrothermal) one, by minerals of the binary systems Au–Ag and Au–Pd as well as mercury, lead, and silver tellurides. Sudburyite and testibiopalladite have been first found in the Krutoi ore occurrence; moreover, testibiopalladite has been first discovered in the Pai-Khoi Ridge. Their chemical compositions and Raman spectra have been examined. The results of sulfide sulfur, oxygen, and carbon isotope studies of calcium-containing minerals of chalcopyrite–quartz veinlets suggest assimilation of the material of the host deposits by the ore-forming mantle fluids. The fluid inclusions in the veinlets are divided into nitrogen–methane and carbon dioxide–nitrogen according to the composition of the gas phase. It has been established that the mineral-forming fluids were poorly saturated with gas. Magnesium and calcium salts were predominant in them. The temperature of the formation of quartz in the chalcopyrite–quartz veinlets is close to 300–490 ºC, and sphalerite–chalcopyrite and associated late gold–telluride–palladium mineralization formed at temperatures not exceeding 260 ºC.

Synthesis of Imines by Selective Oxidation of Amines on alloy nanoparticles of palladium and gold under visible light irradiation at ambient temperatures

Imines are important intermediates in organic synthesis. To avoid derivatives, the research on direct oxidized amines as an alternative method is imminent. The gold (Au)–palladium (Pd) alloy nanoparticles (NPs) catalyst shows a favourable activity and high selectivity on benzylamine oxidation reaction under light irradiation. The yield of the reaction on the alloy NPs with a Au:Pd ratio of 1:1.86 in the dark was 36% at 45 °C, while the yield increased to 95% under light illumination. The study demonstrates different properties from alloy NP to pure Au NP and Pd NP catalysts which may be caused by increased surface charge heterogeneity in the alloy system. The conversion rate of the reaction can also be enhanced by light irradiation and heat. The light energy which utilized by Localized Surface Plasmon Resonance effect of gold in alloy system can highly enhanced the efficiency of reaction. These findings provide useful guidelines for designing efficient alloy catalysts with a plasmonic metal and a catalytically active transition metal for various organic syntheses driven by sunlight.

Synthesis and characterisation of Pd(ii) and Au(i) complexes with mesoionic carbene ligands bearing phosphinoferrocene substituents and isomeric carbene moieites.

While numerous functional ligands combining phosphine and imidazole-2-ylidene (or imidazolin-2-ylidene) donor moieties have already been reported, the chemistry of the corresponding functional mesoionic carbenes (MIC) derived from 1,2,3-triazoles remains nearly untapped. This contribution describes the synthesis of two isomeric series of triazolium salts bearing 1'-(diphenylphosphino)ferrocenyl substituents by [3 + 2] cycloaddition of a P-protected phosphinoferrocene alkyne with azides, or alternatively of a P-protected phosphinoferrocene azide with terminal alkynes, and by subsequent methylation. These salts were used to synthesize structurally unique Pd(ii) complexes featuring a P,C-chelating triazolylidene carbene ligands and Au(i)-MIC complexes with free phosphine groups. The latter were further utilised to prepare Pd(ii)Au(i) heterometallic complexes containing bridging ferrocene phosphino-carbenes as structurally flexible, donor-unsymmetric metalloligands. In addition, the reactivity of the newly prepared, P-protected phosphinoferrocene alkyne Ph2PfcC[triple bond, length as m-dash]CH·BH3 (fc = ferrocene-1,1'-diyl) was investigated, and representatives from all reported compound classes were structurally characterised.

Bimetallic Au-Pd alloy nanoparticles supported on MIL-101(Cr) as highly efficient catalysts for selective hydrogenation of 1,3-butadiene.

Gold–palladium (Au–Pd) bimetallic nanoparticle (NP) catalysts supported on MIL-101(Cr) with Au : Pd mole ratios ranging from 1 : 3 to 3 : 1 were prepared through coimpregnation and H2 reduction. Au–Pd NPs were homogeneously distributed on the MIL-101(Cr) with mean particle sizes of 5.6 nm. EDS and XPS analyses showed that bimetallic Au–Pd alloys were formed in the Au(2)Pd(1)/MIL-101(Cr). The catalytic performance of the catalysts was explored in the selective 1,3-butadiene hydrogenation at 30–80 °C on a continuous fixed bed flow quartz reactor. The bimetallic Au–Pd alloy particles stabilized by MIL-101(Cr) presented improved catalytic performance. The as-synthesized bimetallic Au(2)Pd(1)/MIL-101(Cr) with 2 : 1 Au : Pd mole ratio showed the best balance between the activity and butene selectivity in the selective 1,3-butadiene hydrogenation. The Au–Pd bimetallic-supported catalysts can be reused in at least three runs. The work affords a reference on the utilization of a MOF and alloy nanoparticles to develop high-efficiency catalysts.

Optimization of gold-palladium core-shell nanowires towards H2O2 reduction by adjusting shell thickness.

Designable bimetallic core–shell nanoparticles exhibit superb performance in many fields including industrial catalysis, energy conversion and chemical sensing, due to their outstanding properties associated with their tunable electronic structure. Herein, Au–Pd core–shell (AurichPd@AuPdrich) nanowires (NWs) were synthesized through a one-pot facile chemical reduction method in the presence of cetyltrimethyl ammonium bromide (CTAB) surfactant. The thickness of the Pd shell could be adjusted by directly controlling the Au/Pd feeding ratio while maintaining the nanowire morphology. The as-obtained Au75Pd25 core–shell NWs with a thin Pdrich shell showed significantly enhanced activities towards the reduction of hydrogen peroxide with the sensitivity reaching 338 μA cm−2 mM−1 and a linear range up to 10 mM. In sum, Pd shell thickness could be used to adjust the electronic structure, thereby optimizing the catalytic activity.

Observing the structure-dependent electrocatalytic activity of bimetallic Pd-Au nanorods at the single-particle level.

We developed an electrochemiluminescence (ECL) microscopy technique to image the structure-dependent electrocatalytic reactivity of bimetallic Pd-Au nanorods (NRs) at the single-particle level.

Pd–Au bimetallic catalysts supported on ZnO for selective 1,3-butadiene hydrogenation

The effect of the ZnO morphology on the properties of Pd–Au bimetallic catalysts has been discussed.

Electrocatalytic activity of Pd–Au nanoalloys during methanol oxidation reaction

Methanol fuel cells are very promising power source due to its high efficiency and low emissions of pollutants but their commercialization is hindered by development of the effective catalysts. Bimetallic nanostructured catalysts have been used to increase the effectiveness of methanol electrooxidation. Their high electrocatalytic activity can be accounted largely by the difference in electronegativity of two metals (e.g. Pd and Au), that resulting in gradual Auδ+→Auδ– transition with the increase in Pd content. Therefore, gold-enriched bimetallic Pd-Aunano were recommended as catalysts for oxidation processes since they are characterized by the presence of Auδ+ on their surface. Deposition of Pd, Au and Pd–Au nanoparticles (~50–350 nm) were carried out in dimethyl sulfoxide by pulsed mode of electrolysis directly on electrode surface. Cyclic voltammetry was the main method to study catalytic properties of the modified electrode in the anode oxidation process of methanol. It was found that oxidation rate on the electrode surface modified by bimetallic Pd–Au nanoparticles is ~1.5 times higher as compared to that in the case of electrodes modified by Pd or Au monometallic nanoparticles individually. In order to find highly active, selective, and stable catalysts for methanol electrocatalytic oxidation reaction additional studies are needed to understand the role of electrode surface charge and local OH− ions concentration from alkali solution.

Interdiffusion during heteroepitaxial Au growth on Pd thin films by electroless Au plating (ELGP) at room temperature

Electroless Au plating (ELGP) on Pd thin films is performed. The ELGP time dependence on the surface morphology is investigated by a scanning electron microscope. Continuous nucleation and growth of hemispherical Au islands are observed as the plating time increases. Heteroepitaxial growth of the electroless plated Au on the Pd surface is confirmed by cross-sectional scanning transmission electron microscope images. Cross-sectional energy-dispersive X-ray spectroscopy reveals interdiffusion between the Pd atoms and the plated Au atoms at room temperature, which allows the formation of Au–Pd alloys. The heteroepitaxial Au growth on Pd is significant for reducing contact resistance of Au/Pd structures.

Trace Element Distribution in Magnetite Separates of Varying Origin: Genetic and Exploration Significance

Magnetite is a widespread mineral, as disseminated or massive ore. Representative magnetite samples separated from various geotectonic settings and rock-types, such as calc-alkaline and ophiolitic rocks, porphyry-Cu deposit, skarn-type, ultramafic lavas, black coastal sands, and metamorphosed Fe–Ni-laterites deposits, were investigated using SEM/EDS and ICP-MS analysis. The aim of this study was to establish potential relationships between composition, physico/chemical conditions, magnetite origin, and exploration for ore deposits. Trace elements, hosted either in the magnetite structure or as inclusions and co-existing mineral, revealed differences between magnetite separates of magmatic and hydrothermal origin, and hydrothermal magnetite separates associated with calc-alkaline rocks and ophiolites. First data on magnetite separates from coastal sands of Kos Island indicate elevated rare earth elements (REEs), Ti, and V contents, linked probably back to an andesitic volcanic source, while magnetite separated from metamorphosed small Fe–Ni-laterites occurrences is REE-depleted compared to large laterite deposits. Although porphyry-Cu deposits have a common origin in a supra-subduction environment, platinum-group elements (PGEs) have not been found in many porphyry-Cu deposits. The trace element content and the presence of abundant magnetite separates provide valuable evidence for discrimination between porphyry-Cu–Au–Pd–Pt and those lacking precious metals. Thus, despite the potential re-distribution of trace elements, including REE and PGE in magnetite-bearing deposits, they may provide valuable evidence for their origin and exploration.

One-pot synthesis of Pd20-xAux nanoparticles embedded in nitrogen doped graphene as high-performance electrocatalyst toward methanol oxidation

Mixed Pd–Au bimetallic nanoparticles embedded nitrogen doped graphene composites (PdAu/NG180) are explored for efficient electrocatalytic oxidation of methanol. A simple hydrothermal one-pot polyol method, involving simultaneous reduction of both Pd and Au, is utilized for the synthesis of Pd20-xAux/NG180 (x wt % = 0, 5, 10 and 15). This method is of multiple advantages such as inexpensiveness, reagent-free and environment-friendly being surfactant free. The morphology, crystal structure and chemical composition of NG180, Pd/NG180 and Pd20-xAux/NG180 catalysts are analyzed by XRD, FESEM-EDX, TEM, XPS and Raman spectroscopy methods. Electrocatalytic activities of PdAu/NG180 nanocomposites toward methanol oxidation reaction (MOR) in alkaline media are investigated by cyclic voltammetry, chronoamperometry and CO stripping measurements. Pd20-xAux/NG180 exhibited an increase in the electroactive surface area of Pd to twice by the coexistence of Au. In cyclic voltammetry studies, Pd10Au10/NG180 catalyst exhibits highest peak current density for MOR and is 1.5 times highly efficient compared to Pd20/NG180 with an enhanced shift in the onset potential by 140 mV to lower overpotentials. Besides, Pd10Au10/NG180 catalyst exhibited enhanced electroactive surface area and long-time durability in comparison to Pd20/NG180 catalyst. The steady state current density for MOR observed with Pd10Au10/NG180 at the end of 4000 s (98 mA mg−1Pd) is higher than those observed with all the other catalysts at the end of mere 1000 s alone (97, 61, and 32 mA mg−1Pd). The promising high electrocatalytic activity of Pd10Au10/NG180 is well corroborated from CO stripping experiments that the specific adsorption of CO onto Pd10Au10/NG180 (0.71 C m−2) is merely half to that observed onto Pd20/NG180 (1.49 C m−2).

Formation of drop-shaped inclusions based on Pt, Pd, Au, Ag, Bi, Sb, Te, As during crystallization of the intermediate solid solution in the Cu-Fe-Ni-S system

The phase and chemical composition of drop-shaped inclusions in directionally crystallized intermediate solid solution was studied. The initial melt contained (in mol.%): Fe 31,79; Cu 15,94; Ni 1,70; S 50,20; Sn 0,05; As 0,04; Pt, Pd, Rh, Ru, Ag, Au, Se, Te, Bi, Sb 0,03. Experimental data indicate the simultaneous crystallization of two types of liquids upon cooling of the initial sulfide melt. One of them is formed in the subsystem (Pd, Au, Ag)-(Bi, Sb, Te), and the second - in the subsystem Cu-(S, Bi, Sb, Te). When these liquids solidified, inclusions formed, which we divided into four classes. Class I has a eutectic-like structure with a matrix of Pd(Bi,Sb)xTe1-x solid solution and Au crystallites with Ag, Cu, and Pd impurities. Class II is formed from sulfosalts with inclusions of Bi and Au. Class III includes inclusions of sperrylite Pt(As,S)2. Class IV forms compound inclusions from fragments of classes I-III. The experiment described in the work showed a more complex behavior of noble metals and metalloid impurities during the crystallization of complex sulfide-metalloid melts compared with the previously described data of isothermal experiments.

Decomposition of Methanol on Supported Pd–Au Catalyst for Recovery of Unused Waste Heat at Low Temperature

Decomposition of Methanol on Supported Pd–Au Catalyst for Recovery of Unused Waste Heat at Low Temperature

One-Pot Myrtenol Amination over Au, Au–Pd and Pd Nanoparticles Supported on Alumina

One-pot bio-based myrtenol amination was studied in the presence of alumina supported Au, Au–Pd and Pd nanoparticles subjected to the thermal treatment under oxidizing or reducing atmosphere. Myrtenol amination with aniline was carried out under nitrogen atmosphere (9 bar) at 453 K using toluene as a solvent. The effect of the active metal along with the influence of redox pre-treatment on the catalytic behavior in the hydrogen borrowing reaction was explored. The catalyst characterization was done by transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, nitrogen adsorption. The active metal and the catalysts redox pretreatment affected more noticeably selectivity to the reaction products rather than myrtenol conversion. Monometallic Au/Al2O3 catalyst promoted predominantly formation of the target secondary amine and the corresponding imine without a significant impact of the side reaction of C=C bond hydrogenation in myrtenol, whereas monometallic Pd catalyst activated C=C bond resulting in its hydrogenation. At the same time in the presence of Au–Pd simultaneous hydrogenation of both C=C and C=N bond occurred. Au–Pd catalysts activated in oxygen and hydrogen showed different catalytic activity determined by the composition of surface active sites. Monometallic gold catalyst was more effective in the hydrogen transfer in the case of substrates with competitive unsaturated functional groups.

Stability of ternary nanocrystalline alloys in the Pt–Pd–Au system

Binary alloys have frequently been found to exhibit nanostructured states that are stabilized against grain growth when the minority alloying element strongly segregates to grain boundaries, thereby reducing the grain boundary excess energy. This concept has been formalized in several theoretical frameworks that are now used to design stable nanocrystalline binary alloys. In this work, we consider the extension of such a framework to ternary alloy systems. By considering pairwise interactions between atoms in ternary systems, we identify an experimental system, Pt–Au–Pd, and produce combinatorial alloy films in this system to evaluate their stability against grain growth. In several of these nanostructures stability against grain growth up to 400 °C is observed due to the co-segregation of Au and Pd solutes to the grain boundaries. This result is in line with calculations of a grain boundary energy-based estimation of stability after extending the analysis to account for the nontrivial ternary interaction.

Design and Simulation of a Palladium-Aluminum Nanostructure-Based Hydrogen Sensor With Improved Figure of Merit

We present Palladium (Pd) and Aluminum (Al) nanostructure-based hydrogen sensor in infrared region. Dip strength, full width half maximum, and figure of merit (FOM) are considered for designing the sensor. We numerically demonstrated Pd and Al combination is the appropriate choice for hydrogen sensing as it provides narrow reflection curve in comparison to the reflection curves of Pd–Au combination. Replacing Au by Al, FOM becomes twice. To further improve the performance of the sensor, we optimize the Pd grating depth using rigorous coupled wave analysis method. Using optimized grating depth, FOM could be increased to about 25%. Duty cycle of the structure has also been optimized. FOM of the sensor with optimized parameters is 0.343, and which is about six times higher than that of previously reported grating-based sensor. This proposed sensor can be used for remote sensing of hydrogen gas.

Molecular and Dissociative Adsorption of Oxygen on Au-Pd Bimetallic Clusters: Role of Composition and Spin State of the Cluster.

Utilization of molecular oxygen as an oxidizing agent in industrially important reactions is the ultimate goal to design environmentally benign processes under ambient conditions. However, the high thermal stability and a large O–O dissociation barrier in O2 molecule pose a great challenge toward its successful application in the oxidative chemistry. To achieve this goal, different catalysts based on monometallic and bimetallic clusters have been developed over the years to promote binding and dissociation of molecular oxygen. The successful design of efficient metal cluster catalysis needs an in-depth knowledge of synergistic effects between different metal atoms and intrinsic catalytic mechanisms for O2 adsorption and dissociation. Here, we present a systematic theoretical investigation of reaction pathways for O2 adsorption and dissociation on Au8, Pd8, and Au8–nPdn (n = 1–7) nanoclusters in different spin states. The density functional calculations point out that the O2 dissociation barriers can be significantly reduced with the help of certain bimetallic clusters along specific spin channels. Our results particularly indicate that Au5Pd3 and Au1Pd7 show very large O2 binding energies of 1.76 and 1.69 eV, respectively. The enhanced O2 binding subsequently leads to low activation barriers of 0.98 and 1.19 eV along the doublet and quartet spin channels, respectively, without the involvement of any spin flip-over for O2 dissociation. Furthermore, the computed O2 dissociation barriers are significantly low as compared to the already reported barriers (1.95–3.65 eV) on monometallic and bimetallic Au–Ag clusters. The results provide key mechanistic insights into the interaction and dissociation of molecular oxygen with Au–Pd clusters, which can prove informative for the design of efficient catalysts for oxidative chemistry involving molecular oxygen as a reactant.

Design of a Pd–Au Nitrite Reduction Catalyst by Identifying and Optimizing Active Ensembles

Nitrate (NO3–) is a ubiquitous contaminant in groundwater that causes serious public health issues around the world. Though various strategies are able to reduce NO3– to nitrite (NO2–), a rational catalyst design strategy for NO2– removal has not been found, in part because of the complicated reaction network of nitrate chemistry. In this study, we show, through catalytic modeling with density functional theory (DFT) calculations, that the performance of mono- and bimetallic surfaces for nitrite reduction can be rapidly screened using N, N2, and NH3 binding energies as reactivity descriptors. With a number of active surface atomic ensembles identified for nitrite reduction, we have designed a series of “metal-on-metal” bimetallics with optimized surface reactivity and a maximum number of active sites. Choosing Pd-on-Au nanoparticles (NPs) as candidate catalysts, both theory and experiment find that a thin monolayer of Pd-on-Au NPs (size: ∼4 nm) leads to high nitrite reduction performance, outperforming pu...

Structural and electronic feature evolution of Au-Pd bimetallic catalysts supported on graphene and SiO2 in H2 and O2

The structure and electronic feature evolution of graphene (Gr)- and SiO2-supported Au-Pd bimetallic nanoparticles (NPs) in H2 and O2 at different temperatures were investigated with a series of techniques and DFT calculation method. It was found that a uniform Au-Pd alloy nanostructure was formed on Gr, while a Au@Pd core-shell structure was generated on SiO2. The formation of Au-Pd alloy nanostructure on Gr originates from a strong s-p-d hybridization among Au 5d6s, Pd 4d and Gr C 2p, which greatly facilitates the electron transfer among Au, Pd and Gr and enhances the reduction of palladium species. The higher stability of the geometric and electronic structures of Au-Pd NPs on Gr than on SiO2 in both H2 and O2 atmospheres below 100 °C results from the fact that Gr could timely supplement the electrons transferring to O2 from metallic species in O2-treatment process, but play a contrary role in H2-treatment process. Such unique geometric and electronic structures endow Au-Pd/Gr show higher catalytic activity than Au-Pd/SiO2 in selective oxidation of methanol to methyl formate. A further investigation of catalytic mechanism reveals that the activation of O2 is dominated by the methanol-assisted way on Au and Au-Pd alloy NPs, whereas the direct dissociation of O2 mainly occurs on Pd and Au@Pd NPs.

Gold and Palladium Mediated Bimetallic Catalysis: Mechanistic Investigation through the Isolation of the Organogold(I) Intermediates

Au–Pd based catalytic systems are a unique couple due to the carbophilic Lewis acidity of Au and the redox properties of Pd. To gain more insight into this bimetallic couple, a synthetic and mechanistic investigation was conducted. As key substrates, ynamides (N-alkynyl allyloxycarbamates and N-alkynyl ethyloxycarbamates) were used. Essential for the mechanistic part was the isolation of the organogold(I) intermediate to validate the proposed mechanism. In total, 18 polysubstituted oxazolones and 12 organogold(I) complexes were synthesized.